1. Field of the Invention
The present invention relates to a solid-state imaging device having a microlens and sealing resin on the microlens.
2. Description of the Prior Art
As for a solid-state imaging device using a CCD (Charge Coupled Device), the area of a photodiode serving as a light-receiving portion has been decreased because of requests for decrease in size and improvement in resolution. To compensate the deterioration of a condensing efficiency due to decrease of the area of the light-receiving portion, the so-called microlens has been developed and used.
The microlens is normally made of resin and set above a light-receiving portion formed for each pixel to directly refract light not incoming to the light-receiving portion, to condense the light in the light-receiving portion, and to improve the condensing efficiency and the sensitivity.
However, because the microlens is weak in humidity, it is necessary to protect the microlens by any means when the lens is used under a severe condition such as high temperature and high humidity. For example, the official gazette of Japanese Patent Laid-Open No. 5-41506 discloses a structure in which a microlens is covered with resin and moreover, cover glass for sealing the resin is used.
However, at the time of selecting a sealing resin for. covering a microlens by considering heat resistance, transparency, spectral performance, and refractive-index change, it is unavoidable to select a resin almost the same as the material of the microlens and thereby, the refractive index of the sealing resin becomes almost equal to that of the microlens. As a result, problems occur that the condensing effect of the microlens deteriorates and the light reaching the microlens cannot be completely condensed on a photodiode.
Though an action for increasing a refractive index of a microlens or improving a condensing effect by decreasing a refractive index oaf sealing resin is taken, it is impossible to solve the problems such as the above heat resistance, transparency, spectral performance, and refractive-index change.
The present invention is achieved to solve the conventional problems and its object is to provide a solid-state imaging device having a high condensing efficiency even for a structure using a sealing resin.
The 1st invention of the present invention (corresponding to claim 1) is a solid-state imaging device comprising:
a light-receiving portion for receiving light;
a microlens formed on said light-receiving portion and having a predetermined first refractive index;
a thin-film lens formed on the microlens; and
a resin portion formed on the thin-film lens and having a predetermined second refractive index,
wherein the refractive index of the thin-film lens is smaller than the first and second refractive indexes, and
the,thin-film lens is made of an inorganic material.
The 2nd invention of the present invention (corresponding to claim 2)is a solid-state imaging device comprising:
a light-receiving portion for receiving light;
a microlens formed on the light-receiving portion and having a predetermined first refractive index;
a thin-film lens formed on the microlens; and
a resin portion formed on the thin-film lens and having a predetermined second refractive index,
wherein the refractive index of the thin-film lens is smaller than the first and second refractive indexes, and
the thin-film lens is a flat member made of resin curved along a curved face of the microlens.
The 3rd invention of the present invention (corresponding to claim 3) is the solid-state imaging device according to 1st or 2nd inventions, wherein the first and second refractive indexes are substantially equal to each other.
The 4th invention of the present invention (corresponding to claim 4) is the solid-state imaging device according to 1st invention, wherein
the thin-film lens is a lens made of fluoride and/or oxide.
The 5th invention of the present invention (corresponding to claim 5) is the solid-state imaging device according to 1st or 2nd inventions, wherein the microlens is a lens made of resin.
The 6th invention of the present invention (corresponding to claim 6) is the solid-state imaging device according to 5th invention, wherein
the first and second refractive indexes are close to 1.56 and the refractive index of the thin-film lens ranges between 1.36 or more and 1.50 or less.
The 7th invention of the present invention (corresponding to claim 7 to 11) is the solid-state imaging device according to any one of 2nd to 6th inventions, wherein the thin-film lens is made of resin, the microlens has a diameter of approx. 4000 nm, and the thin-film lens has a thickness of 80 nm or more to 1000 nm or less.